The present invention relates to a rectangular type battery. In particular, the invention relates to a rectangular type battery comprising a positive electrode and a negative electrode laminated on each other with a separator interposed between them, and also to a sealed battery such as a lithium ion battery.
In devices and equipment using batteries, a battery accommodating compartment designed in form of rectangular parallelepiped is generally used. When a cylindrical battery is accommodated in the battery accommodating compartment in form of rectangular parallelepiped, there is a problem in that ineffective volume is increased. Further, diameter of the cylindrical battery is limited by the thickness of the battery accommodating compartment. For this reason, in small-size or thin-walled devices or equipment, a rectangular type sealed battery with smaller thickness is used instead of a cylindrical type battery.
In these batteries, capacity of the battery depends on the quantity of active components in the positive electrode and the negative electrode laminated on each other with a separator interposed between them. The positive and the negative electrodes are produced as follows: A positive electrode active component and a negative electrode active component, each on a belt-like metal base, are coated on each of a positive electrode current collector and a negative electrode current collector respectively. By increasing the coating thickness of the active components, it is possible to increase electric capacity of the positive electrodes and the negative electrodes.
A battery element is prepared by laminating the positive electrode and the negative electrode on each other via a separator, and this battery element is accommodated in a battery case. When the thickness of active component layers of the positive and the negative electrodes is increased in the battery, the swelling or the expansion of the battery case when the battery is charged is unavoidably increased.
When the swelling of the battery case is increased, there may be difficulties in disposing the battery on the devices or equipment where the battery is used or ineffective space may be increased in order to provide surplus space to cope with the anticipated swelling.
JP-07183010(A) describes a method for manufacturing a rectangular type sealed battery. In this method, a side surface of an external case of the battery in contact with the battery element is designed in recessed form.
However, in a battery with smaller thickness where the side surface is merely depressed, it is difficult to attain sufficient effect.
It is an object of the present invention to provide a rectangular type battery, by which it is possible to prevent swelling or expansion of the side surface of the battery case caused by swelling of the battery element when the battery is charged, and also to eliminate useless or ineffective space in the battery accommodating compartment.
The present invention provides a sealed battery, accommodating a battery element of flat shape, said battery element comprising a positive electrode and a negative electrode being laminated on each other with a separator interposed between them and being wound together, characterized in that a recessed portion is formed on a side surface of a battery case running in parallel to a flat surface of the battery element, said recessed portion having a central axis running in parallel to said flat surface and being positioned on a surface passing through the center of the battery case and running perpendicularly to the surface in parallel to the flat surface of the battery element.
Also, the present invention provides the sealed battery as described above, wherein a vertical wall surface is designed in form of a small curved surface, and said wall surface connecting an end of the recessed portion in form of curved surface on an opening of the battery case with a side surface in parallel to the flat surface of the battery element in the battery case, and a distance from the wall surface to the opening end of the battery is gradually reduced toward the center.